1. Field of the Invention
The present invention relates to a method of manufacturing a composite member, particularly, to a method of manufacturing a composite member having a flexible substrate, a multi-layered wiring board, an interposer, a fine wiring pattern such as three-dimensional wiring, an antenna, a coil, a sensor and a fine wiring pattern such as a micromachine. The present invention also relates to a photosensitive composition and a porous base material suitable for use in the manufacturing method of the composite member of the present invention.
2. Description of the Related Art
The present invention also relates to a method of manufacturing a composite member having a conductive portion such as wiring formed in an insulating body and used in the fields of, for example, electric appliances, electronic appliances and communication, to a photosensitive composition suitable for use in the manufacturing method of the composite member, to an insulating body used for the manufacture of the composite member, and to a composite member.
A method that permits manufacturing a fine wiring pattern at low cost is absolutely necessary for the miniaturization of electronic appliances such as portable telephones and a wearable computers. The method of manufacturing a wiring pattern at low cost is also indispensable for the manufacture of, for example, DNA chips and various sensors. Also, for the manufacture of various antennas and coils, it is necessary to form wiring a three-dimensionally on a steric member. The manufacturing technology of such a three-dimensional wiring is also important in the case of forming wiring on the casing of an electronic appliance and for the wiring on a micromachine or an optoelectronic device.
The wiring pattern is manufactured in general by forming a Cu layer on a substrate, followed by etching the Cu layer with a resist pattern used as a mask. However, this technology is troublesome. In addition, it is difficult to form a fine wiring pattern and a three-dimensional wiring pattern by this technology. Proposed as a method of manufacturing a wiring pattern, which permits forming three-dimensional wiring at low cost, is a method of selectively applying an electroless plating to the light exposed portion or unexposed portion. In this method, a photosensitive layer formed on a substrate is exposed to light so as to form a pattern of an ion-exchange group, followed by allowing the ion-exchange group to adsorb metal ions or a metal colloid. Then, an electroless plating is applied with the adsorbed metal ions or the metal colloid used as the catalytic nucleus of the plating so as to form a wiring pattern.
This technology permits eliminating the resist pattern formation and the etching so as to render the process very simple, with the result that the manufacturing cost can be lowered. In addition, this technology makes it possible to achieve easily miniaturization of the wiring pattern and the formation of a three-dimensional wiring pattern. However, a serious problem remains unsolved in this technology. It should be noted that, in order to perform satisfactory plating, it is necessary to increase the adsorption amount of the catalytic nuclei. If the amount of the ion-exchange groups is increased in order to increase the adsorption amount of the catalytic nuclei, the photosensitive layer is dissolved in the plating solution and, thus, tends to peel off. It is certainly possible to avoid the peeling of the photosensitive layer by modifying the surface of the substrate so as to introduce directly the ion-exchange groups as disclosed in, for example, Japanese Patent Disclosure (Kokai) No. 7-207450 or Japanese Patent Disclosure (Kokai) No. 11-246977, or by using as a photosensitive layer the monomolecular layer of the ion-exchange groups chemically coupled with the substrate surface, as disclosed in, for example, Japanese Patent Disclosure No. 6-202343. However, since the amount of the ion-exchange groups is small, the adsorption amount of the catalytic nuclei is not sufficiently large, resulting in failure to achieve satisfactory plating. In conclusion, the conventional method is incapable of satisfying simultaneously both the improvement in the adsorption amount of the catalytic nuclei and the improvement in the resistance of the photosensitive layer to the plating solution.
As described above, the conventional selective electroless plating is low in cost and certainly permits forming a three-dimensional wiring pattern. However, this conventional method gives rise to the problem that, if the amount of the ion-exchange groups is increased in order to increase the adsorption amount of the catalytic nuclei, the photosensitive layer is dissolved in the plating solution.
Incidentally, it was customary in the past to form the via in steric wiring as follows. In the first step, a via hole is formed in an insulating body by a photolithography process using a photosensitive polyimide or resist. Then, a via is formed by selectively applying plating to the via hole or by loading a conductive paste in the via hole. Forming a via by this method requires a resist coating step, a light exposure step and an etching step. Therefore, the via formation is laborious and it is difficult to improve the yield.
In another method of the via formation, a via hole of a predetermined size is formed in an insulating body by using a drill or a CO2 laser, followed by applying plating to the via hole or loading a conductive paste in the via hole. In the method utilizing formation of a via hole in an insulating body, however, it is difficult to form freely a fine via not larger than scores of microns in a desired position.
In the method disclosed in Japanese Patent Disclosure No. 7-207450 referred to previously, a compound having hydrophilic radicals is allowed to permeate the pores of a three-dimensional porous film such as a PTFE film. Under this condition, the three-dimensional porous film is selectively exposed to light in a pattern by using a low-pressure mercury lamp having wavelengths of 185 nm and 254 nm. As a result, hydrophilic radicals are formed on the three-dimensional porous film. Further, metal plating is applied to the three-dimensional porous film.
In the conventional method described above, however, light having a short wavelength is used for the light exposure, with the result that the material constituting the three-dimensional porous film is caused to deteriorate. An additional problem to be noted is that the light used for the light exposure is absorbed by the three-dimensional porous film, resulting in failure to permeate deep inside the porous body. It follows that it is impossible to form a fine via.
Another method of forming a via is disclosed in U.S. Pat. No. 5,498,467. In this method, the entire surface of an insulating body made of a porous material is impregnated with a photosensitive composition containing a photosensitive reducing agent, a metal salt, etc., followed by applying an after-pattern light exposure so as to reduce the cation of the metal salt in the light-exposed portion into a metal nucleus. Then, the photosensitive composition in the unexposed portion is removed by washing, followed by applying electroless plating or soldering to the residual metal nuclei so as to form vias of a predetermined pattern.
In the conventional method described above, however, the entire surface of an insulating body formed of a porous material is impregnated with a photosensitive composition containing a metal salt. Therefore, it is difficult to remove completely the metal salt adsorbed on the portion corresponding to the unexposed portion after the light exposure. It follows that a phenomenon that metal nuclei are precipitated on an undesired portion takes place in the subsequent reducing step. The abnormal precipitation of the metal nuclei gives rise to a problem in the insulating characteristics between the adjacent vias and between the adjacent wiring layers in accordance with miniaturization of the pattern.